The invention relates to an rpm-measuring system with a revolving, areawise magnetized rotor, integrated into a wheel seat of a motor vehicle.
A similar object for example is known from EP 0 518 157 A1. An rpm-measuring system is described there, whose sensor and magnetized rotor are installed on an anti-friction bearing. The revolving outer ring of the anti-friction bearing has the magnetized rotor on one of its end faces. The sensor is disposed opposite the rotor in the axial direction. In this case, the former is fastened inside a ring, which is attached to the inner ring of the anti-friction bearing. For this purpose it has a profile which, on the one hand extends around the sensor, and on the other hand is cantilevered over the outer ring of the anti-friction bearing. Between the edge of the cantilevered section and the cylindrical outer surface of the outer ring of the anti-friction bearing there is a small gap, in front of which a magnet is disposed at a short distance.
The magnet serves the purpose of attracting and collecting magnetic or magnetizable dirt, for example break abrasion and other particles or flakes generated during the normal course of wear and tear, before they reach the magnetized rotor of the rpm-measuring system through the small gap and possibly disturb the effectiveness of the sensor.